How many buns are you talking about? Will they all be in one large pen? Or multiple, small ones? Here's my thought - if you're ok with cleaning & filling them a couple times per day, those might work. But, bunnies are playful, curious critters, who get bored, easily, and they will most likely find a way to get them off the pen, and they'll throw them around, gnaw on them, etc. I used one like this:
https://www.amazon.com/Petmate-Replendish-Microban-Automatic-Available/dp/B0057LE454/ref=sr_1_22?dchild=1&keywords=Continuous+feed+metal+pet+hopper&qid=1588510933&sr=8-22
If the buns will all be together, I'd just get 1 medium to large one for every 4 or 5 buns. If they'll be separated, the smaller hopper style ones will still make your life much easier - just get the smaller ones, and find a way to secure them to the sides of their pens. This gravity feed style works better for water, too. Slightly messier than the upside down bottles, but they'll drink more from a bowl, so they'll be less inclined to get dehydrated, especially when it's hot out. Again, if you use smaller ones, I'd be sure to secure them to the pens.
1
